HOUSTON — Increased rail transport and more pipeline infrastructure for oil from unconventional U.S. plays are narrowing the gap between international and domestic oil prices, the U.S. Energy Information Administration says.

The spread had been growing since the beginning of 2011, reaching $23 in February of this year as pipeline congestion created a glut of U.S. benchmark West Texas Intermediate that sent its price down relative to Brent crude, the international benchmark. Both are graded as light, sweet crude.

More recently, the price gap has been in the $6-to-$10 range because of new pipeline capacity at Cushing, Okla., a key trading hub that has been a choke point for domestic oil. On Monday, the difference shrank to less than $5 a barrel during the trading session for the first time in about 21/2 years.

“Every time we put in a new pipeline or something happens that loosens the bottlenecks, there are giant price aberrations that get alleviated,” said Amy Myers Jaffe, executive director for Energy and Sustainability at the University of California, Davis.

Pipeline and rail projects added in the past two years have allowed oil to flow from North Dakota's booming Bakken Shale and West Texas plays to Gulf Coast refineries, bypassing Cushing.

And while several new pipelines are under construction in areas without a long history of crude production, where transportation infrastructure is scarce, the move to rail has been key to getting oil to market quickly.

“The difference now is that you are having such a volume of new production that the swing transport has become rail,” said Campbell Faulkner, chief data analyst at OTC Global Holdings, an international energy brokerage company. “It is relatively cheap and it's fast. That has helped the market be dynamic and has rebalanced it.”

Before 2011, Brent and West Texas Intermediate prices tracked closely, typically less than $5 apart, with the slightly higher Brent reflecting costs to transport it to the U.S. market, the Energy Information Administration said in a report last week.

The gap narrowed to as little as $4.77 a barrel during the trading session Monday. It's the first time the spread between the two grades has been at $5 or less since Jan. 18, 2011, on an intraday basis, according to data compiled by Bloomberg.

WTI for August delivery advanced $1.43, or 1.5 percent, to $97.99 a barrel on the New York Mercantile Exchange, the highest settlement since June 19. Brent for August settlement increased 84 cents, or 0.8 percent, to end at $103 a barrel on the London-based ICE Futures Europe exchange. Brent's premium over WTI closed at $5.01, the lowest settlement since Jan. 4, 2011.

But federal forecasters are predicting that planned maintenance in the North Sea this summer will reduce production of Brent crude, pushing its price up and potentially widening the Brent-West Texas spread.

And while new pipelines and rail cars have reduced the domestic crude backlog, continued limitations in storage and infrastructure connecting new unconventional plays to the Gulf Coast likely mean a continuing U.S.-international oil price gap.